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Liu, Junyi

Publications and source records attributed to Liu, Junyi.

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

New formation and fate of Isoprene SOA markers revealed by field data-constrained modeling

Particulate 2-methyltetrols (2-MT) and 2-methylglyceric acid (2-MG) are typically used to indicate the abundance of isoprene-derived secondary organic aerosols (SOA). However, their formation and fate are not fully understood. In this study, we showed that particulate 2-MT and 2-MG collected at multiple monitoring sites under a wide range of atmospheric and emission conditions, with concentrations spanning six orders of magnitudes, are well reproduced with an expanded isoprene-SOA scheme implemented into the Community Multiscale Air Quality (CMAQ) model. The scheme considers their three-phase (gas-aqueous-organic phase) partitioning, formation from acid-driven multiphase reactions, and degradation by OH radicals in the gas and aqueous phases. The model results reveal that a non-aqueous formation pathway or direct biogenic emission is needed to supplement the commonly assumed acid-driven multiphase reaction process to explain the observed 2-MT concentrations. This missing pathway contributes to 20–40% of 2-MT in areas with aerosol pH < 2 and more than 70% under less acidic conditions (pH~2–5), such as those encountered in the western US and China. The typical summertime gas-phase photochemical lifetimes of 2-MT and 2-MG are estimated to be 4–6 and 20–30 h, respectively, and their aqueous lifetimes are approximately 20–40 h. Our simulations show that predicted 2-MT is mainly influenced by its aqueous phase loss to OH, but 2-MG is more sensitive to gas phase OH loss due to the preferential partitioning of the two tracers in the aqueous and gas phases, respectively.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Tetragonal C 24 : a topological nodal-surface semimetal with potential as an anode material for sodium ion batteries

Na-ion batteries, as an alternative to Li-ion batteries, have gained increasing attention due to the abundance of sodium and its low cost. In the present work, we prepare a 3D porous carbon material by inserting hexagonal carbon rings into sp 3 C–C bonds in a previously established 3D-(4,4) lattice, termed tC 24 . Ab initio calculations uncover that not only is tC 24 thermally, dynamically and mechanically stable, but it also exhibits a unique electronic band structure with two topological nodal surfaces traversing through the whole Brillouin zone. More importantly, tC 24 is the first all carbon topological nodal-surface semimetal for Na-ion batteries, exhibiting a high theoretical capacity of 232.65 mA h g -1 , a low diffusion energy barrier for Na ions, an appropriate average voltage of 0.54 V and a negligible volume change (~0.94%) during charging/discharging operation. These properties provide tC 24 with a potentially long cycling life when used as an anode material for Na-ion batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Discovery of a high-pressure phase of rutile-like CoO 2 and its potential as a cathode material

Due to the structural failure of layered CoO 2 , there has been considerable effort to improve the reversible capacity of commercial LiCoO 2 cathode materials. Using a global structural search, we have discovered a rutile-like CoO 2 phase as the ground state at 50 GPa. The material is thermally, mechanically and dynamically stable, even after removing the pressure. We show that, when lithiated, this LiCoO 2 material can serve as an improved cathode material for Li-ion batteries. Its many advantages include good structural stability against transition metal migration and oxygen loss, one-dimensional channels for Li ion diffusion with variable energy barriers (0.36–0.86 eV), enhanced ionic mobility, and good intrinsic electronic conductivity brought about by its metallic band structure. Furthermore, with a voltage platform of 3.2–3.8 V, it provides better stability against conventional carbonate solvents than conventional layered cathode materials (>4.0 V). All these features demonstrate that the non-layered CoO 2 phase synthesized at high pressure would be a promising cathode material, providing a performance beyond that of the currently used layered phase.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Superhalogen-based lithium superionic conductors

The development of cheap, durable, and safe inorganic solid electrolytes with superionic conductivity is the key for the next generation of all-solid metal-ion batteries. The recent discovery of antiperovskites with composition Li 3 OA (A = halogen) shows promise in this regard. Here, we demonstrate the potential of a new class of antiperovskites where halogens are replaced by BH 4 superhalogens. In addition to maintaining the high ionic conductivity of Li 3 OA, Li 3 O(BH 4 ) is lightweight, mechanically flexible, thermodynamically more stable, and electronically more insulating than Li 3 OA. By mixing BH 4 with Cl to make Li 3 O(BH 4 ) 0.5 Cl 0.5 , we further show that the conductivity will be doubled. The Li + -ion conductivity of the new materials is of the order of 10 -4 to over 10 -3 S cm -1 at room temperature and will be well above 10 -2 S cm -1 at higher temperatures below the melting point. The conduction mechanism of the material is revealed by identifying the relationship between the orientational symmetry of the BH 4- rotors and the potential surface felt by the lithium ions.

Fang, Hong↗